1. Field of the Invention
The present invention relates to a mechanical power outputting apparatus.
2. Description of the Related Art
Conventionally, there has been proposed a mechanical power outputting apparatus of this type that is equipped with a capacitor connected with a positive pole bus and a negative pole bus of an inverter circuit that imposes a three-phase alternating current on a dynamo-electric motor, and the mechanical power outputting apparatus is also equipped with a direct-current power supply connected with the positive pole bus or the negative pole bus of the inverter circuit and a neutral point of the dynamo-electric motor (see for example, Japanese Laid-Open Patent Publication No. Hei 10-337047, Japanese Laid-Open Patent Publication No. Hei 11-178114, and the like). The apparatus regards a circuit constituted of the coil of each phase of the dynamo-electric motor and a switching element of each phase of the inverter as a boosting chopper circuit that stores electric charge in the capacitor by boosting the voltage of the direct-current power supply. Besides, the apparatus regards the charged capacitor as the direct-current power supply for driving the dynamo-electric motor. The control of the driving of the dynamo-electric motor and the control of the charging to the capacitor are simultaneously performed by the switching actions of the switching elements of the inverter circuit that are performed at the time of the imposition of the three-phase alternating current on the dynamo-electric motor.
However, because such a mechanical power outputting apparatus drives the dynamo-electric motor with the boosted and charged capacitor that is regarded as the direct-current power supply, an actually used direct-current power supply may be one supplying a lower voltage than a voltage necessary for driving the dynamo-electric motor, but the capacitor is required to have a high withstand voltage. The high withstand voltage capacitor is large in size and high in cost, and further that causes the increase of the size and the cost of the mechanical power outputting apparatus.
Moreover, the conventional mechanical power outputting apparatus can drive a single dynamo-electric motor with the direct-current power supply of a low voltage, but it is difficult for the conventional mechanical power outputting apparatus to drive a plurality of dynamo-electric motors separately with the direct-current power supply of the low voltage.
Moreover, the conventional mechanical power outputting apparatus has a probability of a large current pulsation being generated in the current that flows into or flows out from the neutral point of the dynamo-electric motor to increase the loss of the dynamo-electric motor. In a pseudo-three-phase alternating current formed by pulse width modulation (PWM) control using two voltage levels of a positive voltage and a negative voltage, a so-called zero voltage vector output state arises in which each phase voltage is the same . When the zero voltage vector is output, because the potential at the neutral point of the dynamo-electric motor is fixed by the direct-current power supply, a large current flows through a neutral point-connected line of the dynamo-electric motor. Because the zero voltage vector takes two states, i.e. a state that any phase takes a positive voltage and a state that any phase takes a negative voltage, the direction of the current flowing through the neutral point-connected line of the dynamo-electric motor differs depending on which state the zero voltage vector is based. As a result, the large current pulsation is generated on the neutral point-connected line of the dynamo-electric motor.
An object of the present invention is to make a mechanical power outputting apparatus small in size and cheap in cost, and to improve the durability thereof and the stability thereof.
In a mechanical power outputting apparatus of the present invention, an electric power supplying section as a direct-current power supply is connected with either the positive pole bus or the negative pole bus of an inverter circuit, and the electric power supplying section is also connected with the neutral point of a dynamo-electric motor, and a charging section capable of charging and discharging is connected with the other bus between the positive pole bus and the negative pole bus of the inverter circuit that is not connected with the electric power supplying section, and the charging section is also connected with the neutral point of the dynamo-electric motor. Consequently, the electric power supplying section and the charging section connect the positive pole bus and the negative pole bus of the inverter circuit in series, and then it is possible to drive the dynamo-electric motor on the supposition that the electric power supplying section and the charging section are an integrated direct-current power supply. A circuit constituted of the coil of each phase of the dynamo-electric motor and a switching element of each phase of the inverter circuit can charge the charging section by the use of the electric power of the electric power supplying section by means of the switching operation of the switching element, and the charging of the charging section and the driving of the dynamo-electric motor can be performed simultaneously by synchronization of the switching operation with the switching operation at the time of the driving of the dynamo-electric motor. Moreover, because the withstand voltage of the charging section is a value that is a result of the subtraction of the voltage of the electric power supplying section from a voltage necessary for driving the dynamo-electric motor, the withstand voltage of the charging section can be lower than the withstand voltage of a capacitor connected with the positive pole bus and the negative pole bus of the inverter circuit. As a result, the charging section can be realized to be small in size and cheap in cost, namely the mechanical power outputting apparatus can be realized to be small in size and cheap in cost, and further the durability and the stability of the mechanical power outputting apparatus can be improved because the charging section is made to have a low withstand voltage.
Moreover, in the mechanical power outputting apparatus of another aspect of the present invention, a circuit constituted of the coil of each phase of a first dynamo-electric motor that performs the rotation thereof and the driving thereof by a polyphase alternating current and a switching element of each phase of a first inverter circuit can be regarded as a circuit that boosts the voltage of a first electric power supplying section by means of the electric power of the electric power supplying section to store charge in a charging section, and further the charging section can be regarded as a direct-current power supply capable of driving the first dynamo-electric motor and a second dynamo-electric motor. That is, the circuit constituted of the coil of each phase of the first dynamo-electric motor and the switching element of each phase of the first inverter circuit can charge the charging section by the use of the electric power of the first electric power supplying section by means of the switching operation of the switching elements of the first inverter circuit, and the charging of the charging section and the driving of the first dynamo-electric motor can be performed simultaneously by synchronization of the switching operation with the switching operation at the time of the driving of the first dynamo-electric motor. Still further, the second dynamo-electric motor can be driven to rotate by the switching operation of the switching elements of the second inverter circuit by means of the electric power stored in the charging section. Moreover, because the switching operation of the first inverter circuit and the switching operation of the second inverter circuit can be performed separately, the first dynamo-electric motor and the second dynamo-electric motor can be driven separately. That is, a plurality of dynamo-electric motors can separately be driven by the use of the electric power supplying section of a low voltage.
According to the mechanical power outputting apparatus of still another aspect of the present invention, a driving current is made to be a pseudo-polyphase alternating current of voltage levels of three steps or more, i.e. voltage levels of a positive voltage, a negative voltage, and an intermediate voltage in between these two, and consequently the probability of the appearance of the zero voltage vector where the voltage of each of the phases are the same voltage, but different from the voltage of a second power supply, can be largely decreased, and the probability of the appearance of current pulsations that can be generated at the neutral point of a dynamo-electric motor can be decreased. As a result, the loss of the dynamo-electric motor can be suppressed.
According to the mechanical power outputting apparatus of a yet another aspect of the present invention, a driving current is made to be a pseudo-polyphase alternating current of voltage levels of three steps or more, and consequently the probability of the appearance of the zero voltage vector, the voltage of each phase of which is the same voltage but different from the voltage of a second power supply, can be largely decreased, and the probability of the appearance of current pulsations that can be generated at the neutral point of a dynamo-electric motor can be decreased. As a result, the loss of the dynamo-electric motor can be suppressed.
According to the mechanical power outputting apparatus of a further aspect of the present invention, the switching of a plurality of switching elements in an inverter circuit is controlled on the basis of the modulated wave of each phase based on the voltage command of each phase of a polyphase alternating current and on the basis of the carrier wave of each phase having a prescribed phase difference between each other corresponding to each phase of the polyphase alternating current, and consequently the probability of the appearance of the zero voltage vector, the voltage of each phase of which is exactly the same voltage but different from the voltage of a second power supply, can be largely decreased, and the probability of the appearance of current pulsations that can be generated at the neutral point of a dynamo-electric motor can be decreased. As a result, the loss of the dynamo-electric motor can be suppressed.
According to the mechanical power outputting apparatus of a still further aspect of the present invention, the switching of a plurality of switching elements in an inverter circuit is controlled on the basis of the modulated wave of each phase based on the voltage command of each phase of a polyphase alternating current and on the basis of the carrier wave of each phase having a prescribed phase difference between each other corresponding to each phase of the polyphase alternating current, and consequently the probability of the appearance of the zero voltage vector the voltage of each phase of which is the same voltage can be decreased, and the probability of the appearance of current pulsations that can be generated at the neutral point of a dynamo-electric motor can be decreased. As a result, the loss of the dynamo-electric motor can be suppressed.